The basic principle of fiberoptic transducers involves shining a light on a reflective surface and measuring how much light is reflected back. It is known that the amount of light that is reflected is determined by the distance that the reflective surface is located from the light source and the light collector used.
In general, fiberoptic transducers use one or more fibers to channel light from a light source to and reflect off a reflective surface and uses one or more fibers to collect the reflected light from the reflected surface and channel it to a measuring device. Fiberoptic transducers have been used for optical pyrometry as disclosed in U.S. Pat. No. 4,468,771 and for measuring a quantity of heat applied to the end of an exposed fiber portion of an optical fiber as disclosed in U.S. Pat. No. 5,009,513.
The present invention relates to a fiber optic temperature transducer that may be located in the end of a small tube for measuring temperatures in remote or difficult areas to access, such as for determining the temperature in a particular area of a human body and which area might be accessed by a flexible tube inserted in a blood vessel and guided to the appropriate area of the body. The present transducers also may be used safely for measuring temperatures in areas where an electrical spark may cause combustible gases on liquids to ignite.
The fiberoptic temperature transducer in accordance with the present invention includes a temperature measuring system involving an electronic control unit, a reflecting member attached to, or part of, a rod made of a first material, the remote end of the rod with the reflecting member being free to move within a tubular member made of a second material. The other end of the rod is attached to the tubular member. At least one optical fiber is carried by a support member in the tubular member and extends therethrough. The end of the at least one optical fiber is spaced from the reflective member so as to create a gap. The first and second materials are chosen, based upon their respective coefficients of thermal expansion, such that a change in temperature of both materials will cause the length of the gap to either decrease or increase linearly, thereby causing a change in the amount of light that is reflected and detected by the optical fiber. Two optical fibers may be used if desired. One transmits the light to the reflective surface and the other receives it from the reflective surface and transmits it to the processing system. The sensitivity of the temperature measuring capability is determined by choosing the length of the rod in conjunction with the type of first and second materials used. The output signal of the collecting optical fiber is conditioned and processed by the electronic control unit and the temperature measurement can be displayed on a digital or analog readout.
Thus it is an object of the present invention to provide a fiberoptic temperature transducer.
It is also an object of the present invention to provide a fiberoptic temperature transducer that has first rod member surrounded in spaced relationship with a second coaxially aligned tubular body member with the first rod member having a first thermal coefficient of expansion and the second tubular body member having a second thermal coefficient of expansion. A cylindrical fiberoptic support member is spaced from and axially aligned with the first rod member in the tubular body member such that with a change in temperature, the difference in expansion or contraction of the materials of the first rod member and the second tubular body member causes the amount of space between the first rod member and the support member to vary. A reflecting surface on the end of the first rod member faces the support member and at least one optical fiber is attached to the end of the support member facing the first rod member, such that the amount of light reflected from the reflecting surface to the optical fiber varies with a change in temperature and thus a change in the space between the first rod member and the support member.
It is still another object of the present invention to provide a temperature transducer wherein the materials having the first and second thermal coefficients of expansion have properties such that the change in gap length between one body member and a support member caused by expansion is a substantially linear change with a change in temperature.
It is yet another object to the present invention to provide a temperature transducer with a tubular member formed of a material having a first thermal coefficient of expansion and a cylindrical rod formed of a material having a second thermal coefficient of expansion and inserted in and attached at only one end to the tubular member for expansion within the tubular member and wherein the length of the cylindrical rod varies with the materials chosen for the rod and the tubular member to determine the sensitivity of the temperature measuring capability within a chosen temperature operating range.